1. Field of the Invention
This invention relates to porous moldings and more particularly, to moldings of accumulated mass made of stringy or thready extrudates of porous materials.
2. Description of the Prior Art
In recent years, applications of porous inorganic materials have rapidly been developed and such materials are now widely employed mainly in the fields such as filter media, adsorbents, acoustic materials, heat-insulating materials, carriers for catalyst and the like. The applications in these wide fields have been found to produce problems with respect to the handling and effects of materials when the materials are used as they are. Accordingly, they have been frequently employed after molding into pellets, beads, rings or honeycombs. These moldings are properly selected depending on the end use. For instance, in applications where the pressure loss must be avoided such as with carriers for catalyst, the honeycomb structure is favorably employed. In this connection, however, the honeycomb structure is greatly restricted from the viewpoint of the manufacture technique and since the processing techniques such of dies and molding rollers have their own limitations, it is almost impossible to obtain a structure having more than a certain degree of fineness. For instance, with the molding process using dies, the thickness of cell wall is limited to about 100.mu. and even with the roller molding means, it is difficult to make the thickness below 50.mu.. After all, it is generally accepted that the limit of the number of cells per square inches is about 1000. Under these circumstances, attention has been again given to pellets or beads, which are admixed with binders and then press molded. These press moldings contain very fine voids or interstices therein, showing an advantage that when this molding is used, for example, as carrier for catalyst, the effective surface area becomes much larger than that of the molding of the honeycomb structure. However, it is necessary to use binders two times at the stage of molding pellets themselves and the stage of the secondary molding and thus there is a fear that such binders give adverse influences not only on the porosity of product but also on mechanical strengths. In addition, the press molding is conducted after once molded pellets have been reduced to pieces and sifted and thus requries twice the steps even in molding operation, inviting the rise of processing cost.